Page:Treatise on poisons in relation to medical jurisprudence, physiology, and the practice of physic (IA treatiseonpoison00chriuoft).pdf/429

 lead was the cause of them, it was long before the source of the poison was discovered. Every vessel and article used in the kitchen was in vain examined; when at length it was discovered that the sugar used by the family had been taken from a barrel which had formerly contained white lead, and that, as the sugar from the centre of the barrel had been dug out, and given away to various friends, the outer part of it next the white lead was chiefly used by the family themselves.

Process for detecting Lead in Organic Mixtures.

In the first place, a little nitric acid should be added to the suspected matter before filtration; for nitric acid redissolves any insoluble compound formed by the salts of lead with albumen and other animal principles, as well as some of those formed with vegetable principles; and consequently renders it more probable, that the poison will be detected in the first part of the analysis, if present at all. This being done, sulphuretted-hydrogen gas is to be transmitted through the fluid part of the mixture; and if a dark-coloured precipitate is formed, the whole is to be boiled and filtered to collect the precipitate.

In order to ascertain that the precipitate positively contains lead, those who are accustomed to use the blowpipe may put the sulphuret into a little hole in a bit of charcoal, and reduce it by the fine point of a blowpipe-flame; when a single globule is procured, which is easily distinguished by its lustre and softness. A better process, for those not accustomed to the blowpipe, and perhaps a better test of the existence of lead in all circumstances, is to heat the sulphuret to redness in a tube, and to treat it with strong nitric acid, without heat or with the aid of a gentle heat only. The lead is thus dissolved without the sulphur being acted on. The solution is then to be diluted with water, filtered, evaporated to dryness, and gently heated to expel the excess of nitric acid. If the residue be dissolved in water, it will present the usual characters of a lead solution when subjected to the proper liquid tests. Of these the hydriodate of potass is to be preferred when the quantity is too small for trying more of them. But for this purpose care must be taken to expel all the excess of nitric acid, because an excess will strike a yellow colour with the test though lead be not present.

If the preceding process should not detect lead in the filtered part of the mixed fluid, then the insoluble matter left on the filter is to be incinerated, and the residuum dissolved in nitric acid, and tested as above. This branch, however, will be rarely required, if lead be present, because the precaution of adding nitric acid, previous to filtration, dissolves the lead from most of its compounds which are insoluble in water. The process of incineration in medico-legal ana-*